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LASER POLISHING OF METALS
F R A U N H O F E R I N S T I T U T E F O R L A S E R T E C H N O L O G Y I LT
DQS certified by
DIN EN ISO 9001
Reg.-No.: DE-69572-01
Fraunhofer-Institut
für Lasertechnik ILT
Director
Prof. Reinhart Poprawe
Steinbachstraße 15
52074 Aachen, Germany
Telephone +49 241 8906-0
Fax +49 241 8906-121
info@ilt.fraunhofer.de
www.ilt.fraunhofer.de
Fraunhofer Institute for Laser Technology ILT
The Fraunhofer Institute for Laser Technology ILT is worldwide
one of the most important development and contract research
institutes of its specific field. The activities cover a wide range
of areas such as the development of new laser beam sources
and components, precise laser based metrology, testing
technology and industrial laser processes. This includes laser
cutting, caving, drilling, welding and soldering as well as
surface treatment, micro processing and rapid manufacturing.
Furthermore, the Fraunhofer ILT is engaged in laser plant
technology, process control, modeling as well as in the
entire system technology. We offer feasibility studies,
process qualification and laser integration in customer
specific manufacturing lines. The Fraunhofer ILT is part
of the Fraunhofer-Gesellschaft.
Contact
Dr. Edgar Willenborg
Telephone +49 241 8906-213
edgar.willenborg@ilt.fraunhofer.de
Subject to alterations in specifications and other technical information. 04/2018.
Tool and Mold Making
For the processes used in tool and mold making, the state
of the art is manual polishing, which has processing times of
often more than 10 min/cm². Therefore, there is a great need,
particularly in this industry, for automated polishing processes
for complex 3D surfaces. The roughness it requires is often in
the range of Ra = 0.05 to 0.3 µm.
On the tool steels 1.2343, 1.2311, 1.2379 and 1.3207, laser
polishing can be used to smooth milled and eroded surfaces
with a roughness of Ra = 1 to 4 µm down to a roughness of
Ra = 0.05 to 0.2 µm. The surface rate here is about 1 cm²/min,
but can be increased to up to 10 cm²/min by material-adapted
intensity distributions. Injection molding and embossing tools
with laser-polished surfaces have comparable service lives to
those of manually polished tools.
In addition, when the process parameters are modulated, the
gloss level on tool surfaces can be adjusted with high local
resolution (150 μm), which also makes it possible to produce
two-color and multi-gloss effects. In leather grain, for example,
only the recesses of the grain are polished in the tool, the
webs remain unprocessed.
Deburring and Shape Melting
Burrs and edges can be removed by laser machining and
remelted as a function of the requirements. In this case, when
a defined shape is melted, for example, uniform rounding can
be achieved.
Medical Technology
Titanium materials are often used in medical technology. While
these can be polished with conventional, cutting processes,
there is a great expenditure of time and personnel. When
this process is automated using laser polishing, machining
time and cost can be significantly reduced. Laser-polished
surfaces have a high degree of geometrical accuracy owing
the principle involved and, therefore, allow tight tolerances.
The absence of grinding and polishing agents also means that
the surfaces have a high chemical purity after laser polishing,
which is particularly important for implants.
On diamond-milled surfaces with an initial roughness of
Ra ≈ 0.3 μm, a roughness of Ra ≤ 0.1 μm can be achieved
when polished with pulsed laser radiation. The processing
time is only 3 s/cm² and, thus, significantly shorter than that
of manual polishing.
Range of Materials
Laser polishing is particularly well suited for nickel, titanium
and cobalt/chromium alloys. Even with an initial roughness
in the range Ra = 1 to 15 μm, a roughness of Ra < 0.2 μm
can be achieved with an area rate of 1 to 5 cm²/min. Other
steels and cast alloys can also be polished. The polishing result
depends on the material and its homogeneity.
Machine Technology and CAM-NC Data Chain
Together with partners from the industry, Fraunhofer ILT
has developed a machine tool for laser polishing of complex
3D components. The laboratory results and experience have
been transferred to a robust machine technology suitable for
industrial production. The basis is a five-axis portal machine,
which positions the workpieces and performs slow feed
movements. In combination with a highly dynamic three-axis
laser scanner, the machine can reach the required process
speeds of up to 1 m/s.
Due to the machine kinematics with 5+3 axes, special demands
are placed on the CAM-NC data chain. Fraunhofer ILT develops
solutions that enable the user to use a well-known CAM
system for milling, but also for path planning in laser polishing.
A downstream technology processor, which combines the
functions of a post-processor with specific adjustments, con-
verts the milling paths into laser polishing paths. The 3D laser
scanner is controlled by a flexible software system that can
be seamlessly integrated into the NC control of the machine.
The machine and the CAM-NC data chain are available for
component- and application-specific test series at Fraunhofer ILT.
1 Machine tool for laser polishing.
2 Dual gloss effect on selectively polished
leather grain.
3 Laser-polished active surface cutout
of a slide for die casting.
4 Partially laser-rounded sheet edges made
of stainless steel (sheet thickness 1.5 mm).
5 Unprocessed and laser-polished knee joint,
produced additively.
LASER POLISHING OF METALS The Fraunhofer Institute for Laser Technology ILT uses laser radiation to automatically polish components
with complex 3D surfaces. With this new process, users from various industries, such as those from tool and
mold industry or medical technology, can avoid tedious manual processing and save both money and time.
The Process
When laser radiation is used to polish metals, a thin surface
layer of the workpiece is remelted and the surface smoothed
due to interfacial tension. The innovation of laser polishing
lies in its fundamentally different mode of action (remelting)
compared to conventional grinding and polishing processes
(ablation). For metallic materials, diode-pumped solid-state
lasers are generally used. If the surfaces already have a low
roughness, e. g. after grinding, pulsed lasers with pulse
durations of several 100 ns can be used. If the surfaces are
rougher, e. g. after milling or additive manufacturing, conti-
nuous lasers are used. The remelting depth is between a few
100 nm when pulsed lasers are used and up to 100 μm with
continuous lasers.
Process Features and Advantages
• Automated processing of 3D surfaces
• Polishing result independent of the operator
• High process speeds, especially when
compared to manual polishing
• High reproducibility
• Selective polishing of selected areas
• Low mechanical stress on the components,
because of the non-contact process
• No grinding and polishing waste
• No incorporation of grinding and polishing agents
into the surfaces
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